It is generally known that the pickling effect in metal pickling improves exponentially with temperature. Among other things, pickling times can be significantly shortened when operating at elevated temperatures. Due to very high emissions of the pickling medium (HCl, H.sub.2 SO.sub.4, mixed acids) as well as environmental and ecological considerations, e.g., with respect to corrosion, it has only been possible to temper pickling baths to no more than approximately 25-30.degree. C. until now.
Encapsulated pickling plants or encapsulated pre-treatment plants were developed in order to provide an option for operating pickling baths at higher temperatures. This encapsulated design is intended to prevent emissions from escaping from the region of the pickling or pre-treatment chamber. However, one prerequisite for this type of arrangement is that the pickling or pre-treatment plant is designed in such a way that a permanent vacuum exists. This measure is intended to prevent the emissions from escaping from the pickling or pre-treatment plant. This is also realized by means of a continuous removal of air from the pickling plant or pre-treatment chamber by suction.
The critical time in this known pickling system occurs when hangers need to be transported into the pickling plant, i.e., when a gate leading into the pickling plant is opened. The same situation occurs when removing hangers from the pickling plant if no drying furnace is provided.
In conventional arrangements of the air supply and suction stations, it is disadvantageous that emissions might escape from the pickling plant despite the removal of air by suction, in particular, during the cold season.